# Standard library header <iosfwd>

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This header contains forward declarations for the Input/output library.

### Forward declarations
Defined in header `<string>`
std::char_traits | Class Template which describes properties of a character type (class template)
std::char_traits<char> | (class template specialization)
std::char_traits<wchar_t> | (class template specialization)
std::char_traits<char8_t> (C++20) | (class template specialization)
std::char_traits<char16_t> (C++11) | (class template specialization)
std::char_traits<char32_t> (C++11) | (class template specialization)
Defined in header `<memory>`
allocator | the default allocator (class template)
Defined in header `<ios>`
basic_ios | manages an arbitrary stream buffer (class template)
fpos | represents absolute position in a stream or a file (class template)
Defined in header `<streambuf>`
basic_streambuf | abstracts a raw device (class template)
Defined in header `<ostream>`
basic_ostream | wraps a given abstract device (std::basic_streambuf) and provides high-level output interface (class template)
Defined in header `<istream>`
basic_istream | wraps a given abstract device (std::basic_streambuf) and provides high-level input interface (class template)
basic_iostream | wraps a given abstract device (std::basic_streambuf) and provides high-level input/output interface (class template)
Defined in header `<fstream>`
basic_filebuf | implements raw file device (class template)
basic_ifstream | implements high-level file stream input operations (class template)
basic_ofstream | implements high-level file stream output operations (class template)
basic_fstream | implements high-level file stream input/output operations (class template)
Defined in header `<sstream>`
basic_stringbuf | implements raw string device (class template)
basic_istringstream | implements high-level string stream input operations (class template)
basic_ostringstream | implements high-level string stream output operations (class template)
basic_stringstream | implements high-level string stream input/output operations (class template)
Defined in header `<syncstream>`
basic_syncbuf (C++20) | synchronized output device wrapper (class template)
basic_osyncstream (C++20) | synchronized output stream wrapper (class template)
Defined in header `<spanstream>`
basic_spanbuf (C++23) | implements raw fixed character buffer device (class template)
basic_ispanstream (C++23) | implements fixed character buffer input operations (class template)
basic_ospanstream (C++23) | implements fixed character buffer output operations (class template)
basic_spanstream (C++23) | implements fixed character buffer input/output operations (class template)
Defined in header `<strstream>`
strstreambuf (deprecated in C++98)(removed in C++26) | implements raw character array device (class)
istrstream (deprecated in C++98)(removed in C++26) | implements character array input operations (class)
ostrstream (deprecated in C++98)(removed in C++26) | implements character array output operations (class)
strstream (deprecated in C++98)(removed in C++26) | implements character array input/output operations (class)
### Typedefs and specializations
std::streampos | std::fpos<std::char_traits<char>::state_type>
std::wstreampos | std::fpos<std::char_traits<wchar_t>::state_type>
std::u8streampos | std::fpos<std::char_traits<char8_t>::state_type>
std::u16streampos | std::fpos<std::char_traits<char16_t>::state_type>
std::u32streampos | std::fpos<std::char_traits<char32_t>::state_type>
In addition, for each class template `std::basic_T` declared in this header, `std::T` and `std::wT` are declared as a synonym of `std::basic_T<char>` and `std::basic_T<wchar_t>` respectively.

### Synopsis

    namespace std {
      template<class CharT> struct char_traits;
      template<> struct char_traits<char>;
      template<> struct char_traits<char8_t>;
      template<> struct char_traits<char16_t>;
      template<> struct char_traits<char32_t>;
      template<> struct char_traits<wchar_t>;

      template<class T> class allocator;

      template<class CharT, class Traits = char_traits<CharT>>
        class basic_ios;
      template<class CharT, class Traits = char_traits<CharT>>
        class basic_streambuf;
      template<class CharT, class Traits = char_traits<CharT>>
        class basic_istream;
      template<class CharT, class Traits = char_traits<CharT>>
        class basic_ostream;
      template<class CharT, class Traits = char_traits<CharT>>
        class basic_iostream;

      template<class CharT, class Traits = char_traits<CharT>,
               class Allocator = allocator<CharT>>
        class basic_stringbuf;
      template<class CharT, class Traits = char_traits<CharT>,
               class Allocator = allocator<CharT>>
        class basic_istringstream;
      template<class CharT, class Traits = char_traits<CharT>,
               class Allocator = allocator<CharT>>
        class basic_ostringstream;
      template<class CharT, class Traits = char_traits<CharT>,
               class Allocator = allocator<CharT>>
        class basic_stringstream;

      template<class CharT, class Traits = char_traits<CharT>>
        class basic_filebuf;
      template<class CharT, class Traits = char_traits<CharT>>
        class basic_ifstream;
      template<class CharT, class Traits = char_traits<CharT>>
        class basic_ofstream;
      template<class CharT, class Traits = char_traits<CharT>>
        class basic_fstream;

      template<class CharT, class Traits = char_traits<CharT>,
               class Allocator = allocator<CharT>>
        class basic_syncbuf;
      template<class CharT, class Traits = char_traits<CharT>,
               class Allocator = allocator<CharT>>
        class basic_osyncstream;

      template<class CharT, class Traits = char_traits<CharT>>
        class basic_spanbuf;
      template<class CharT, class Traits = char_traits<CharT>>
        class basic_ispanstream;
      template<class CharT, class Traits = char_traits<CharT>>
        class basic_ospanstream;
      template<class CharT, class Traits = char_traits<CharT>>
        class basic_spanstream;

      template<class CharT, class Traits = char_traits<CharT>>
        class istreambuf_iterator;
      template<class CharT, class Traits = char_traits<CharT>>
        class ostreambuf_iterator;

      using ios  = basic_ios<char>;
      using wios = basic_ios<wchar_t>;

      using streambuf = basic_streambuf<char>;
      using istream   = basic_istream<char>;
      using ostream   = basic_ostream<char>;
      using iostream  = basic_iostream<char>;

      using stringbuf     = basic_stringbuf<char>;
      using istringstream = basic_istringstream<char>;
      using ostringstream = basic_ostringstream<char>;
      using stringstream  = basic_stringstream<char>;

      using filebuf  = basic_filebuf<char>;
      using ifstream = basic_ifstream<char>;
      using ofstream = basic_ofstream<char>;
      using fstream  = basic_fstream<char>;

      using syncbuf     = basic_syncbuf<char>;
      using osyncstream = basic_osyncstream<char>;

      using spanbuf     = basic_spanbuf<char>;
      using ispanstream = basic_ispanstream<char>;
      using ospanstream = basic_ospanstream<char>;
      using spanstream  = basic_spanstream<char>;

      using wstreambuf = basic_streambuf<wchar_t>;
      using wistream   = basic_istream<wchar_t>;
      using wostream   = basic_ostream<wchar_t>;
      using wiostream  = basic_iostream<wchar_t>;

      using wstringbuf     = basic_stringbuf<wchar_t>;
      using wistringstream = basic_istringstream<wchar_t>;
      using wostringstream = basic_ostringstream<wchar_t>;
      using wstringstream  = basic_stringstream<wchar_t>;

      using wfilebuf  = basic_filebuf<wchar_t>;
      using wifstream = basic_ifstream<wchar_t>;
      using wofstream = basic_ofstream<wchar_t>;
      using wfstream  = basic_fstream<wchar_t>;

      using wsyncbuf     = basic_syncbuf<wchar_t>;
      using wosyncstream = basic_osyncstream<wchar_t>;

      using wspanbuf     = basic_spanbuf<wchar_t>;
      using wispanstream = basic_ispanstream<wchar_t>;
      using wospanstream = basic_ospanstream<wchar_t>;
      using wspanstream  = basic_spanstream<wchar_t>;

      template<class State> class fpos;
      using streampos = fpos<char_traits<char>::state_type>;
      using wstreampos = fpos<char_traits<wchar_t>::state_type>;
      using u8streampos = fpos<char_traits<char8_t>::state_type>;
      using u16streampos = fpos<char_traits<char16_t>::state_type>;
      using u32streampos = fpos<char_traits<char32_t>::state_type>;
    }

    // deprecated
    namespace std {
      class strstreambuf;
      class istrstream;
      class ostrstream;
      class strstream;
    }

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